Burner control circuit protection system



y 1937. B. E. SHAW 2,080,580

BURNER CONTROL CIRCUIT PROTECTION SYSTEM Filed Dec. 2, 1935 CU BRENTSUPPLYZ fiz 22222 [or Patented May 18, 1937 UNITED STATES PATENT OFFICEBurton E. Shaw, Adel,

Iowa, assignor to Penn Electric Switch Company, Des Moines, Iowa, acorporation of Iowa Application December 2, 1935, Serial No. 52,595

8 Claims.

An object of my invention is to provide a protection system of simple,and inexpensive construction for burner control circuits.

A further object is to provide in connection with a burner controlcircuit, a protection system which gives low voltage protection, asingle relay or the like being operable to cut in at as low as 80% ofthe full line voltage, and to cut out at a point not lower thanapproximately 65% of the full line voltage, whereas in the usual systemsin which relays are used for burner control circuits, the relay, whenproperly designed to give sufficient motion for operation of thecontacts, cuts out at about 35% of the full line voltage. This isparticularly important because at about 60% of the full line voltage,the burner functions improperly, its efficiency is low, the air velocityand oil pressure being decreased, and the opening of the solenoid orpressure regulating valve which 20 usually controls the oil supply isrestricted. Also low voltage in the ignition transformer occurs whichcauses entire loss of, or at least irregular, spark. This results in theburner popping and sometimes in an explosion. The problem is par- 25ticularly present in small localities where current consumption variesgreatly, and in most all'localities when sleet gathers on thetransmission wires and causes a temporary drop in voltage, which maylast for sometimes an hour or more. It is, therefore, obvious that cutout of the relay at}; or above 65% of the full line voltage is desirale.

One object of my invention is to provide a relay which can be cut in atone voltage and thereafter maintained in the cut-in position by areduced voltage, so that it is then easier to drop out upon subsequentline voltage drop, and the dropping out of the relay will occur beforean excessive drop in the full line voltage occurs whereas if the initialcurrent supply (instead of a reduced current supply due to such reducedvoltage) were maintained for keeping the relay energized, the linevoltage at which the relay drops out would be excessively low.

A further object is to provide a system which is especially adapted foruse in connection with an anticipating type of room thermostat, so thatthe current flowing through the heater of the thermostat issubstantially proportional to the line voltage regardless of whether asafety switch heater used in connection with the system is either in thecircuit, or out of the circuit.

With these and other objects in view my invention consists in theconstruction, arrangement and combination of the various parts of thedevice, whereby the objects contemplated are attained, as hereinaftermore fully set forth, pointed out in my claims, and illustrated in theaccompanying drawing, in which:

The figure is an electrical diagrammatical view of the system.

I use the -eference character M to indicate a motor or the like of afuel burner. The burner itself is indicated generally at B. Atransformer T is provided having a primary coil l 0 and a secondary coilI2, provided with a tap it intermediate its ends. A room thermostat RTis provided, and this thermostat is illustrated as having ananticipating heater indicated at H. The purpose of the heater H is toslightly raise the temperature of the atmosphere surrounding thetemperature responsive element of the room thermostat so that its higl.temperature response will be to an ambient temperature relatively closeto its low temperature response. This type of thermostat and itsoperation are fully disclosed in the Shafer Patent Number 1,583,496, ofMay 4, 1926. A relay coil R is included in the system and so is acombustion switch CS.

For controlling the main circuit, a safety switch SS is provided, whichis normally closed. It is adapted to be opened by energization of asafety switch heater SSH for apredetermined length of time, as willhereinafter be described.

The room thermostat RT is provided with contacts IS. The relay Rincludes an armature l8 attracted by the coil of the relay when it isenergized, and operable to close holding contacts and motor controlcontacts 22. Thecombustion switch CS may include a leaf spring 24, withthe end of which a notched disk 26 coacts in the manner set forth in theWilliams Patent, Number 827,703, dated October 13, 1931.

Briefly, a bimetal coil 28 has one end anchored to a stationary bearing30, and its other end anchored to the end of a rod 32 on which the disk26 is mounted. The bimetal coil 28 extends into the stack: of a furnaceheated by the burner B, and is thus responsive to combustion. Uponcombustion occurring, the coil 28 unwinds for opening the contacts 34 ofthe combustion switch.

The safety switch is normally closed by an arm 36 held in the positionshown on the drawing by a bimetal latch 38. As the temperature of thesafety switch heater rises, due to energizetion thereof, the bimetallatch 38 warps upwardly and finally after a predetermined period of timepermits a spring 40 to move the arm 36 and separate the contacts .of thesafety switch S8.

Practical operation When the room thermostat RT calls for heat, acircuit is established through the following elements on the drawing: a,H, RT, 16, b, R, c, d, SSH, e, 34, 24 and ,f. The current for thiscircuit is supplied by the entire secondary coil l2. Assuming thesecondary voltage to be 25, then there are 25 volts available forcausing cut-in of the relay. The parts can be so designed that the relaycan cut in at of this value, so that the relay is thus operable atanywhere above 80% of the full line voltage supplied to the primary 0011I0.

As soon as the holding contacts 20 are closed by energization of therelay, two circuits are established. The first, or relay holdingcircuit, includes the following elements: a, H, RT, 16, b, R, c, g, 20,h. and 14. Thus the upper portion of the secondary coil I2 is then theonly source for holding the relay closed. This current, obviously, isweaker than the'initial current from the entire secondary coil l2, andconsequently the gaps in the relay can be quite wide and yet the relaywill cut out upon only a substantially small drop in the normal linevoltage.

The second circuit is established by closing of the holding contacts 20through the following elements: 14, h, 20, g, d, SSH, e, 34, 24 and f.The lower portion of the secondary coil I2 is therefore the source ofcurrent for the safety switch heater with the elements g, 20, h and 14of the relay holding circuit constituting a common return.

If combustion does not occur within the time for which the safety switchis set, the contacts 34 will remain closed and the safety switch willtrip out, thus necessitating remedying the trouble and resetting thesafety switch, or a recycling operation after a purging period if thesystem is designed for such.

If combustion does occur, the contacts 34 will be separated as soon asheat in the stack is sufficient to rotate the disk 26 counter-clockwise.Thereupon only the relay holding circuit will remain established, thesafety heater circuit being broken.

With my circuit I provide a current load for the anticipating heater Hof the room thermostat which is substantially always in proportion tothe line voltage. As soon as the initial circuit is established, thecontacts 20 close, so that the holding circuit for the relay is theneffective through the heater. Thereafter, while the safety switch heateris in the circuit of the lower portion of the transformer secondary, acertain value of currentin proportion to the line voltage willflowthrough the heater H, whereas when the heater SSH is cut out of thiscircuit, the current flow through the circuit for the heater H willremain substantially unchanged. To insure this, the secondary of thetransformer must deliver substantially constant voltage. Therefore it isessential that the impedance of the transformer be negligible incomparison with the load impedance i. e. SSH, R and H. The impedance ofSSH is considerably less than the sum of the impedances of R plus H.There is a very slight difference due to no current flowing through thesafety switch heater circuit, and consequently the strength of the relayholding circuit including the heater H is increased but slightly by thisdifference. According to measurements I have taken, this difference isso very slight that the heater H will produce substantially the sametemperature rise in a given period, whether the combustion switchcontacts 34 are closed or open. In other types of circuits, it has beenimpossible to obtain such a desirable result.

It is thus obvious that with a single relay and a transformer having anintermediate tap, it is possible to utilize a stronger current forinitially closing the relay than is necessary for maintaining it closed,and by using a lower voltage for maintaining it closed, the relay willdrop out at a higher line voltage. At the same time the circuit providescurrent supply for the heater H which is always substantiallyproportional to the line voltage, and also for the heater SSH, thusinsuring proper operation within proper limits of these two heaters whenthey are energized.

It will be seen that my system can be used in a number of ways. AlthoughI have shown one form in which it may be constructed, considerablechange can be made in the details of construction without departing fromthe real spirit and purpose of my invention and it is my intention tocover by my claims, any modified forms of structure or use of mechanicalequivalents, which may be reasonably included within their scope.

I claim as my invention:

1. In a protection system for burners, a transformer, a room thermostat,a relay operable upon energization to cause operation of the burner, a

circuit including the secondary of said transformer and said relay andcontrolled by said room thermostat, said room thermostat establishingsaid circuit upon closure of the room thermostat, and means thereafteroperable to maintain said relay energized from a portion only of saidsecondary.

2. In a protection system for burners, a transformer, a room thermostat,a relay operable upon energization to cause operation of the burner, acircuit including the secondary of said transformer and said relay andcontrolled by said room thermostat, said room thermostat establishingsaid circuit upon closure of the room thermostat, means thereafteroperable to maintain said relay energized from a portion only of saidsecondary, and a combustion switch in circuit with the remaining portionof said secondary and normally closed but opened upon the presence ofcombustion.

3. In a protection system for burners, a transformer, a room thermostat,a relay operable upon energization to cause operation of the burner, acircuit including the secondary of said transformer and said relay andcontrolled by said room thermostat, said room thermostat establishingsaid circuit upon closure of the room thermostat, means thereafteroperable to maintain said relay energized from a portion only of saidsecondary, and a combustion switch and a safety switch actuator in 'theother circuit, said combustion switch being normally closed but openedupon the presence of combustion.

4. In a. protection system for burners, a transformer, an initial roomthermostat circuit, including a room thermostat, means operable uponenergization by the secondary of said transformer to initiate operationof the burner, a safety switch heater and combustion switch contacts,said combustion switch contacts being closed in the absence and open inthe presence of combustion, a safety switch normally closed but openedby said safety switch heater upon energization thereof for apre-determined period of time, a second circuit energized by a portiononly of said secondary of said transformer and including said roomthermostat and said means, holding contacts for establishing said secondcircuit and for maintaining it when said combustion switch contacts areseparated, said holding contacts being closed by energization of saidmeans and a third circuit energized by the remaining portion of saidsecondary and including said holding contacts, said safety switch heaterand said combustion switch contacts, said second and third circuitsbeing established and said initial room thermostat circuit being alteredas to current supplied thereto by closure of said holding contacts, saidcombustion switch contacts upon opening due to combustion establishmentdiscontinuing said third circuit and upon subsequent closure due tocombustion failure reestablishing said third circuit to thereby energizesaid safety switch heater to cause it to open said safety switch.

5. In a protection system for burners, a transformer, an initial roomthermostat circuit including a room thermostat, means operable uponenergization by the secondary of said transformer to initiate operationof the burner and combustion switch contacts, said combustion switchcontacts being closed in the absence and open in the presence ofcombustion, a second circuit energized by a portion only of saidsecondary of said transformer and including said room thermostat andsaid means, holding contacts for establishing said second circuit andfor maintaining it when said combustion switch contacts are separated,

said holding contacts being closed by energization of said means and athird circuit energized by the remaining portion of said secondary andineluding said holding contacts and said combustion switch contacts,said second and third circuits being established and said initial roomthermostat circuit being altered as to the current supplied thereto byclosure of said holding contacts.

6. In a protection system for burners, a transformer having anintermediate tap for furnish ing two sources of current supply, aninitial room thermostat circuit connected across said transformer andincluding a room thermostat, means operable upon energization by closureof the room thermostat vto initiate operation of the burner, a safetyswitch heater and combustion switch contacts in said initial roomthermostat circuit, said combustion switch contacts being closed in theabsence and open in the presence of combustion, a safety switch normallyclosed but opened by'said safety switch heater upon predeterminedenergization thereof, holding contacts closed by energization of saidmeans and connected with said initial room thermostat circuit fordividing it so that upon closure of the holding contacts a secondcircuit is established through said room thermostat and saidmeans, and athird circuit is established through said safety switch heater andsaidcombustionswitchcontacts, said second and thirdcircuits beingtherebyestablished and said initial room thermostat circuit beingaltered as to current supplied thereto, said combustion switch contactsupon opening discontinuing said third circuit and upon subsequentclosing due to combustion failure re-establishing the third circuitwhereby to energize said safety switch heater to cause it to open saidsafety switch.

7. In a protection system for burners, a transformer having anintermediate tap for furnishing two sources of current supply, aninitial room thermostat circuit connected across said transformer andincluding a room thermostat, means operable upon energization by closureof the room thermostat to initiate operation of the burner, a safetyswitch heater and combustion switch contacts in said initial roomthermostat circuit, said combustion switch contacts being closed in theabsence and open in the presence of combustion, a safety switch normallyclosed but opened by said safety switch heater upon predetermined.energization thereof, holding contacts closed by energization of saidmeans and connected with said initial room thermostat circuit fordividing it so that upon closure of the holding contacts a secondcircuit is established through said room thermostat and said means, anda third circuit is established through said safety switch heater andsaid combustion switch contacts, said second and third circuits beingthereby established and said initial room thermostat circuit beingaltered as to current supplied thereto, said combustion switch contactsupon opening discontinuing said "third circuit.

8. A burner control burner, an operating circuit therefor including aburner switch, a source of current for said circuit, a transformerconnected with said source and having a tapped secondary, a roomthermostat and magnetic relay serially connected initially with the endterminals of the secondary, said relay constructed to close said burnerswitch when energized in response toclosure of the room thermostatswitch, and means operated by said relay upon energization thereof toconnect a terminal of the relay with the tap of said secondary tothereby reduce the operating current of said relay and enable the sameto open upon a predetermined minimum fall of line voltage.

\ BURTON E. SHAW.

